Positive Effects of K⁺ Ions on Three-Dimensional Mesoporous Ag/Co₃O₄ Catalyst for HCHO Oxidation

Abstract

Three-dimensional (3D) ordered mesoporous Ag/Co3O4 and K–Ag/Co3O4 catalysts were successfully prepared on the basis of 3D-Co3O4. All catalysts possess 3D mesoporous structures, which are not affected due to Ag and K addition. Ag nanoparticles, uniformly dispersed and supported on the polycrystalline wall of K–Ag/Co3O4, provide sufficient active sites for HCHO oxidation reaction. 1.7% K–Ag/Co3O4 has turnover frequencies (TOFs) of 0.22 s–1 at 60 °C and 2.62 s–1 at 100 °C, and its HCHO conversion at room temperature is 55% (HCHO 100 ppm and GHSV 30000 h–1). The addition of K+ ions obviously promotes the catalytic performance for HCHO oxidation due to surface OH– species provided by K+ ions and more abundant Ag(111) active faces, Co3+ cations and surface lattice oxygen (O2–) species generated by stronger interaction between Ag and Co and anion lattice defects. Ag(111) faces, Co3+ ions, and O2– are active species. Combined with TOFs, at low temperature (<80 °C), the HCHO catalytic activity on K–Ag/Co3O4 catalyst largely depends on the surface OH– species at the perimeter of the Ag(111) facets; at relatively high temperature (>80 °C), the surface OH– species are consumed and replaced quickly, and their supplement relies on the migration of O2– species from 3D-Co3O4 support. The pathway of reaction for HCHO oxidation on the K–Ag/Co3O4 follows the HCHO → CHOO– + OH– → CO2 + H2O route.